Organic solvents, many of which are classified as volatile organic compounds (VOCs), are widely used in traditional inkjet inks. VOCs are compounds of carbon (excluding carbon monoxide, carbon dioxide, metallic carbides or carbonates, and ammonium carbonates) that form ozone through atmospheric photochemical reactions. Compounds of carbon (also known as organic compounds) have different levels of reactivity. That is, various organic compounds do not react at the same speed or contribute to ozone formation to disparate extents.
VOCs are believed to be hazardous to human health because they react with free radicals in the air and generate ozone. Pursuant to the Clean Air Act of 1990, the U.S. Environmental Protection Agency (EPA) has mandated significant changes relating to the use of VOCs in inkjet inks, including mandates to reduce or report the use of VOCs that significantly contribute to the formation of ground level ozone. Generally, the EPA determines whether a given organic compound significantly contributes to the formation of ground level ozone by comparing the reactivity of the given compound to the reactivity of ethane. A VOC is determined to have a “negligible” reactivity if it is proven to not participate in atmospheric photochemical reactions to a lesser extant than ethane.
Unfortunately, most of the organic solvents traditionally used in inkjet inks either do not have the desired properties needed in a coating application or contribute to the formation of ground level ozone to an undesirable extent. Examples of VOCs that have been employed in inkjet inks are methanol, ethanol, and methyl ethyl ketone. A need exists for inkjet inks that do not significantly contribute to the formation of ground level ozone.